Rigid polyurethane foams and processes for their production are known. Such foams are typically produced by reacting an isocyanate with an isocyanate-reactive compound, such as a polyol, in the presence of a blowing agent. Blowing agents known in the art include hydrofluoro-carbons (HFC's), hydrocarbons (HC's), hydrochlorofluorocarbons (HCFC's) and chlorofluorocarbons (CFC's). See for example, U.S. Pat. No. 5,786,400, which discloses a process for preparing a rigid polyurethane foam, in which a polyisocyanate containing a benzene ring is used as the organic isocyanate and a polyether polyol is used as the polyol and wherein the blowing agent is a cyclopentane. Similarly, U.S. Pat. No. 5,539,006 discloses rigid foams with improved insulation and physical properties produced by reacting an organic polyisocyanate with a sucrose-based polyether polyol in the presence of a catalyst and a blowing agent selected from hydrogen-containing fluorocarbons (HFC's) and hydrogen containing chlorofluorocarbons (HCFC's). See also, U.S. Pat. Nos. 5,439,947 and 6,245,826.
However, due to environmental concerns, CFC's have been phased-out, and HCFC's will be phased-out in the coming years. Specific hydrofluorocarbons (HFC's), such as 1,1,1,2-tetrafluoroethane (HFC 134a) and 1,1,1,3,3-pentafluoropropane (HFC 245fa), as well as hydrocarbons, such as cyclopentane, have been selected as the next generation of blowing agents by appliance manufacturers. Also, some HCFC's such as chlorodifluoromethane (HCFC 22) and 1-chloro-1,1-difluoromethane (HCFC 142b) are approved for certain foam applications until 2010. Several of these blowing agents are gaseous, having boiling points below 60° F. and may exhibit poor solubility in polyols, resulting in a significant vapor pressure. Low k-factor foams made with these gaseous or low boiling blowing agents are often difficult to process and tend to have a higher than desired density.